To investigate how solvent (water) and cosolvent (osmolyte) affect protein structure in various osmolyte solutions, in the present study we used GB1p peptide as the model protein to study its folding process in 2,2,2-trifluoroethanol (TFE)∕water and denaturation process in GdmSCN∕water solutions, respectively. It was observed that TFE moderately enhances the structure stability of native β-hairpin, consistent with the previous experimental observation that the hairpin conformation population of several polypeptides is increased in TFE∕water solution compared to in pure water. More interestingly, the formation of β-hairpin is significantly accelerated in TFE∕water solution. The accelerated folding of β-hairpin consists of following sequential events: the accumulation of TFE on protein surface → less water surrounding carbonyl group (easier dehydration of CO) → the formation of CO-NH backbone hydrogen bond. In contrary, the denaturation of hairpin structure of GB1p peptide in GdmSCN∕water solution is induced by the accumulation of Gdm(+) on protein surface and the hydrogen bonding from water as well as Gdm(+). Therefore, this study shows the importance of water in TFE-induced formation and Gdm(+)-induced denaturation of β-hairpin structure.
